The invention relates to a method for the thermo-mechanical regeneration of bulk material, especially of foundry black sand. The heating-up of the black sand that is to be regenerated is effected during its transport in a layer of low height. The invention also relates to arrangement for carrying out the method.
The molding sand used in foundries is used with additional components which help maintain the shape given to the sand. Such a molding sand can, however, at best be reused only in part. Both the acquisition of new sand and the disposal of "black" sand prove unfavorably expensive. In particular, the disposal of the black sand, for example by depositing it in dumps, is made increasingly difficult and expensive due to increasing concern for the environment.
Industrie-anzeiger No. 26 of Mar. 29, 1985, page 32 discloses known thermal, mechanical, wet-chemical and thermo-mechanical methods for the regeneration of black sand. However, in this article the thermal, mechanical and the wet-chemical methods are described as economically unjustifiable. This is because either the regeneration can only be carried out successfully when certain binders are present or only with an unreasonably high expense. Batch operation is recommended using a whirler tool in the form of a rotor in a closed container, in connection with an open flame. The flame grazes the surface of the bulk material and heats it to temperature of maximally 300.degree. C. It was found that, in view of the achievable throughput, an unacceptably high expenditure is required. Furthermore, the desired removal of adhering binder cannot be achieved to the desired extent.
The DE-PS No. 35 16 191 recommends regenerating such bulk materials by sliding them in a dosed, thin layer across floors which allow a heating of the sliding bulk material by infrared rays. Such arrangements are praised as economical, small and compact and especially as flexible regarding the throughput. However, the heat attainable and the throughput capacity have found to be inadequate and uneconomical. The thermal destratification has also been carried on with the aid of fluidized bed furnaces with relatively large capacity. These methods, however, are expensive and only applicable for large amounts of throughput. Moreover, varying dwelltimes of the sand in the furnace arise which additionally reduces the profitability. Further, such fluidized bed furnaces do not guarantee trouble-free operation because heavy foreign bodies, especially casting spatter can settle, with increasing duration of operation, on the furnace bed.
It is a primary object of the invention to provide an efficient, economical arrangement of the kind described whose initial product can be used without restrictions like new sand.